This will appear as an animal or creature figure, like for a charm bracelet, made of stone or ivory. When tested, it will radiate magic, but not a curse, as this item is more broken than cursed. Upon careful inspection and research, it will appear to give the wearer the ability to transform into whatever type of creature is depicted by the charm. This includes statistics, certain abilities, etc., as determined by the GM, or, as in-keeping with a Polymorph spell. The character's base Intelligence and Wisdom remain the same. Previous testing will have allowed for the wearer to return to their normal form, either at will, or after a pre-set time.
Once the transformation is used when it really matters, however, it becomes permanent, while the charm turns black and crumbles away. Polymorphing back to their original form will not be so easy, as it will require a high level Dispel Magic to be cast on the victim, followed by some sort of permanent shape-changing magic.